1. National Institute of Standards and Technology, Div. 847.10, 325 Broadway, Boulder, Colorado 80303, USA
2. Present addresses: Research Electro-Optics , 1855 South 57th Court, Boulder, Colorado 80301, USA (C.J.M.); NIST, Atomic Physics Division (842), 100 Bureau Drive, Stop 8424, Gaithersburg, Maryland 20899-8424, USA (B.E.K.).

Correspondence to: D. J. Wineland Correspondence and requests for materials should be addressed to D.J.W. (e-mail: Email: dwineland@nist.gov).

Abstract

The theory of quantum mechanics applies to closed systems. In such ideal situations, a single atom can, for example, exist simultaneously in a superposition of two different spatial locations. In contrast, real systems always interact with their environment, with the consequence that macroscopic quantum superpositions (as illustrated by the 'Schrödinger's cat' thought-experiment) are not observed. Moreover, macroscopic superpositions decay so quickly that even the dynamics of decoherence cannot be observed. However, mesoscopic systems offer the possibility of observing the decoherence of such quantum superpositions. Here we present measurements of the decoherence of superposed motional states of a single trapped atom. Decoherence is induced by coupling the atom to engineered reservoirs, in which the coupling and state of the environment are controllable. We perform three experiments, finding that the decoherence rate scales with the square of a quantity describing the amplitude of the superposition state.

1. National Institute of Standards and Technology, Div. 847.10, 325 Broadway, Boulder, Colorado 80303, USA
2. Present addresses: Research Electro-Optics , 1855 South 57th Court, Boulder, Colorado 80301, USA (C.J.M.); NIST, Atomic Physics Division (842), 100 Bureau Drive, Stop 8424, Gaithersburg, Maryland 20899-8424, USA (B.E.K.).

Correspondence to: D. J. Wineland Correspondence and requests for materials should be addressed to D.J.W. (e-mail: Email: dwineland@nist.gov).